This Sub-order, though containing animals of much higher organisation than the _Lemuroidea_, embraces species presenting many different grades of intelligence, and ranging in size from the Pigmy Marmoset, not larger than a small Kitten, to the {124}ponderous Gorilla and the genus _Homo_. In external characters the Monkeys and Apes have in general a shorter and less Dog-like nose than the Lemurs, thin lips and a more distinct face; while their eyes, situated on the face, are invariably directed forwards, and never outwards, or to the side. The opening of their nostrils is either outward (as in those inhabiting the New World), or downwards (as in the bulk of the Old World species). All of them are covered with hair; the tail may be long, short, or wanting. The proportions of the fore-limbs to the hind- vary much in the different groups. The great toe, as well as the thumb, is (except in a few species) fully opposable, so that in the majority of members of the Sub-order, the foot is as good a prehensile organ as the hand. From this circumstance comes the designation, _Quadrumana_, or "four-handed," so often applied to these animals. In a few species the thumb is rudimentary or absent, but the fore-finger, the absence of which characterised some of the Lemurs, is always present and well developed, and the corresponding digit in the foot (except in the Marmosets) has a flat nail instead of a claw. The mammæ of the _Anthropoidea_ are always situated on the breast. If we examine the structures underlying the skin, we find that in the skull the orbits are entirely shut in by a bony wall, so that the finger cannot be passed into the temporal depression behind, as could be done in the Lemurine skull, and that the lachrymal foramen opens within the cavity for the eye. In the present Sub-order there is no toothless space in the mid-line of the upper jaw, the incisor teeth being set close together; but there is always a vacuity, except in Man, between the incisors and the canine tooth. The lower canine teeth do not resemble in form the incisors, nor do they protrude horizontally, as in the Lemurs. {125}The two halves of the lower jaw are always co-ossified together, when the animal is full grown. The _humerus_, or arm-bone, never has an entepicondylar foramen on the inner side of its lower portion, and the bones of the fore-arm (the _ulna_ and _radius_) are never ossified together, nor are those of the lower leg (the _tibia_ and _fibula_); so that there is perfect freedom for every movement necessary for grasping and walking, or for rotating the hand or foot on the wrist and ankle. With regard to the brain, the anthropoid cerebrum, or fore-brain, is greatly convoluted, and differs from that of the Lemurs by its proportionately larger size, the cerebellum, or hind-brain, being as a rule entirely covered by it.